FOLATE CHEMOTACTIC RECEPTORS IN DICTYOSTELIUM-DISCOIDEUM .2. GUANINE-NUCLEOTIDES ALTER THE RATES OF INTERCONVERSION AND THE PROPORTIONING OF 4 RECEPTOR STATES
FOLATE CHEMOTACTIC RECEPTORS IN DICTYOSTELIUM-DISCOIDEUM .2. GUANINE-NUCLEOTIDES ALTER THE RATES OF INTERCONVERSION AND THE PROPORTIONING OF 4 RECEPTOR STATES
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DOI：
10.1016/0167-4889(86)90214-4
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发表时间：
1986-04-08
期刊：
影响因子：
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通讯作者：
BULGAKOV, R
中科院分区：
文献类型：
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作者：
DEWIT, RJW;BULGAKOV, R
分析了盘基网柄菌离体膜上叶酸趋化受体的配体结合特性。检测到四种受体状态中的三种（BF、BS 和 BSS），显示速率常数和 Kd 值与完整细胞获得的速率常数和 Kd 值相似。鸟嘌呤核苷酸改变了受体状态的比例以及几种转化的速率。 (i) BFinto BS 的转化受到 GDP 的抑制，但不受鸟苷酰亚胺二磷酸 (GuaPP[NH]P) 或 GTP 的抑制。 (ii) GTP 和 GuaPP[NH]P 降低了 BS 位点的数量。 (iii) GTP 和 GDP 降低了与 BSS 的结合，但 GuaPP[NH]P 增加了与 BSS 的结合。 (iv) GTP 增加了 BSS 的消失率，但 GuaPP[NH]P 没有增加。用 15 mg/ml 牛血清白蛋白处理膜制剂后，未观察到鸟嘌呤核苷酸的影响。这种处理导致检测到与先前描述的类型不同的结合类型。该结合位点的亲和力极高（N10-甲基叶酸的Kd≤0.2nM），而解离相对较慢（k−1≤3·10−4s−1）。有人提出，牛血清白蛋白以不可逆的方式将叶酸受体与鸟嘌呤核苷酸调节（G）蛋白解偶联。提出了一个模型，其中四种受体状态对应于与 G 蛋白和 GDP 或 GTP 的不同相互作用。
The ligand binding properties of folate chemotactic receptors on isolated membranes ofDictyostelium discoideumwere analyzed. Three out of the four receptor states (BF, BSand BSS) were detected, showing rate constants andKdvalues similar to those obtained for intact cells. Guanine nucleotides changed the proportioning of the receptor states as well as the rates of several conversions. (i) The transformation of BFinto BSwas inhibited by GDP but not by guanylyl imidodiphosphate (GuaPP[NH]P) or GTP. (ii) The number of BSsites was lowered by GTP and GuaPP[NH]P. (iii) The binding to BSSwas lowered by GTP and GDP, but increased by GuaPP[NH]P. (iv) The rate of disappearance of BSSwas increased by GTP, but not by GuaPP[NH]P. Effects of guanine nucleotides were not observed after treatment of the membrane preparations with 15 mg/ml bovine serum albumin. This treatment caused the detection of a binding type different from the types described previously. The affinity of this binding site was extremely high (Kd≤ 0.2 nM forN10-methylfolic acid), while the dissociation was relatively slow (k−1≤ 3·10−4s−1). It is proposed that bovine serum albumin uncouples the folate receptor from a guanine nucleotide regulatory (G) protein in an irreversible manner. A model is presented in which the four receptor states correspond to distinct interactions with a G protein and GDP or GTP.